Apparatus for removing excess coating from a poppet valve



y 7, D. K. HA K 2,893,349

APPARATUS FOR REMOVING EXCESS-COATING FROM A POPPET VALVE Filed Nov. 27. 1953 INVENTOR United States Patent APPARATUS FOR REMOVING EXCESS COATING FROM A POPPET VALVE Dean K. Hanink, Birmingham, Micln, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 27, 1953, Serial No. 394,583

4 Claims. Cl. 118-63) This invention relates to coating poppet valves and more particularly to an inexpensive apparatus and process for removing excess molten coating metal from such valves.

With the advent of high compression internal combustion engines and the more extensive use of leaded fuels in recent years, the exhaust valves of internal combustion engines have been subject to rapid oxidation and high temperature corrosion by the hot combusion gases. The gases which result from the burning of leaded gasolines are especially detrimental and greatly shorten valve life. Consequently exhaust valve failure frequently occurs either because of high temperature corrosion of the valve seating face or because of corrosion of the stem immediately beneath the valve head. Severe corrosion of this stem actually results in its necking down to a point where the stem will fracture.

To alleviate, the aforementioned oxidation and corrosion problem and to provide poppet valves which possess a considerably increased operatinglife, these valves may be coated with aluminum. A process for coating valves with aluminum is disclosed in my co-pending patent application S.N. 364,673, filed June 29, 1953. This process provides an aluminum coated valve having at or adjacent its surface a thin layer of an alloy of aluminum or aluminum base alloy and the base metal of the valve. This layer is provided at the valve seating face and also may be provided around the valve head and neck. For best results, the valve should have an extremely thin layer of aluminum or aluminum base alloy over the alloy layer.

In order to provide a poppet valve with a uniformly thin layer of coating metal, it is necessary to remove the excess aluminum or other coating metal while still in a molten condition. Moreover, this sur lus metal must be removed without damage to the valve or the coating layer.

A principal object of the present invention therefore is to provide a simple, practical, and inexpensive apparatus for controlling the thickness of a metallic coating on a poppet valve.

A further object of the invention is to provide a method of effectively utilizing such an apparatus so as to form a poppet valve having aconsiderably increased operating life due to a uniformly thin corrosion-resistant layer of aluminum or aluminum base alloy. This process produces a coated valve of high quality in which there is provided a continuous chemical bond at the interface of the coating metal and the base metal.

The above and other objects are attained in accordance with the present invention by the use of an apparatus which removes from poppet valves excess molten coating metal which would otherwise drain in an irregular manner if the valves were merely allowed to cool after removal from the-coating bath. This apparatus, which provides the valves with a generally uniformly thin coating layer, is a simple, yet effective device which removes any surplus molten coating metal by means of a jet of air or other suitable fluid. Compressed air is preferably used, the air stream being directed so as to remove excess aluminum, for example, in a uniform manner, especially at the seating face, the coated portion of the valve which is most critical. The resultant coating layer is extremely thin and therefore will not spall or flake 01f.

Other objects and advantages of this invention will more fully appear from the following detailed description of a preferred embodiment of the invention, reference being made to the accompanying drawing in which:

Figure 1 is a vertical sectional view, with parts in elevation, of a cylindrical air orifice or air blasting fixture especially designed to remove excess molten coating metal from poppet valves immediately after the coating step to thereby provide thinly coated valves having optimum corrosion resistance properties; and

Figure 2 is a sectional view along the line 2--2 of Figure l.

The alloying of the surface portion of the poppet valve with the coating metal, such as aluminum or aluminum base alloy, may be carried out in any desired manner. The preferred method is to apply molten aluminum or aluminum base alloy to the valve under such conditions that the aluminum will form an alloy with the valve material and result in the desired layer thinness. Best results are obtained when the aluminum or aluminum base alloy is applied by any of the procedures described in Patent No. 2,569,097 Grange et a1., owned by the assignee of the present invention. An especially advantageous method comprises preheating the valve to a'temperature of between approximately 1280 F; and, 1400 F. in a fused salt bath consisting essentially of 37% to 57% KCl, 25% to 45% NaCl, 8% to 20% Na AlF and 0.5% to 12% AlF The valve is thereafter immersed for a short time in a molten bath of aluminum or aluminum base alloy at a temperature of about 1250 F.to 1325 F. Subsequently the valve is removed from the aluminum bath and rinsed for a short period of time not in excess of approximately 15 seconds in the fluxingsalt. The excess coating material is then removed by means of an air blast in accordance with the present invention. As thus treated, the valve is provided with an extremely thin and uniform coating of aluminum bonded to the base metal by an intermediate extremely thin anduniform layer of an alloy of aluminum with the base metal.

A relatively short period of immersion in the aluminumm bath is desirable to prevent excessive formation of brittle iron-aluminum alloys. Ordinarily, therefore, the valve being coated is retained in the molten aluminum or aluminum alloy not more than approximately l0 seconds, a period between 5 and 10 seconds being preferred at present.

The surfaces of the valve to be coated are preferably cleaned prior to the aluminum coating and alloyingoperation. One satisfactory method is to clean the valves in a molten electrolytic caustic salt (such as the commercially available product called Kolene) at a temperature of about 900 F. The valves then may be washed in water and thereafter preferably further cleaned by. acid pickling. A suitable acid pickling bath is an aqueous solution containing about 2% hydrofluoric acid, 7% sulphuric acid and 10% nitric acid. In some instances the valves may require only a simple degreasing treatment in a chlorinated solvent prior to the aluminum coating and alloying operation. Mechanical cleaning methods, such as grit blasting, sand blasting, hydroblasting, etc., may be employed in some cases to supplement the chemical treatment.

The steps of degreasing and pickling the valve are not 3 essential to the process, however, as heating in the fused salt prior to immersion in the aluminum or aluminum alloy bath will provide a clean surfaced valve unless it is exceptionally contaminated to beginwith. 7

After the valves have been cleaned, the portions thereof which are not'to be'coated may be treated with a suitable stop-off coating to'prevent the aluminum from bonding to or allowing with the base metalat such'surfac'es. A suitable stop-01f material for this purpose is a sodium silicate solution, such as an aqueous solution containing 20% to 50% sodium silicate. If the coating metal is to be applied to'the entirehead and neck of the valve, the valve stem is normally coated with such-a sodium silicate solution to within% to 1% inches of the valve head.

When aluminum or an aluminum base alloy is used as the coating material, the alloy of aluminum should containabout 80% or more of aluminum. Hence, the word aluminum, when used in the claims to refer to the coatingmaterial, is intended to include not only pure aluminumor commercially pure aluminum, but also aluminum base alloys containing at least approximately 80% aluminum.

The alloy of aluminum with the valve material should in all cases be extremely thin. In general the layer of alloy should have a thickness of from 0.0005 inchto 0.0015 inch, the outer aluminum layer having a thickness not inexcess of 0.004 inch. It is-presently preferred thatthe layer of the alloy of'aluminumtherewith be not over 0.0015 inch. in thickness.

Any suitable poppet valve material may be satisfactorily provided-with a thin protective coating layer in accordance withthepresent; inventioni; and this coating may be applied. particularly eflectively to the typical ferrous-base materials used to form poppet-valves of internal combustionengines. In the case of aluminum coated steel valves, the interfaciallayer which is formed next to the steel is complex iron-aluminum.

After. thevalve has been dipped. in the fused saltflux and the molten aluminum or aluminum base alloy bath, the formed layer of aluminum. or aluminum alloy is thicker or heavier than desired. By passing the coated valve slowly throughthe molten salt after the aluminum dipping step,- some of the excess molten coating metal may be drained off. However, even after the salt bath rinse which shouldnot exceed approximately 15 seconds in-duration, the molten metal layer is still too thick. Although more of the surplus molten coating metal may be removed by rapidly vibrating or rotating the coated valve during or after removal from'the aluminum or aluminum alloy bath, such procedures frequently result in distortion or improper distribution of the aluminum coating layer on thevalve. Hence an air blast is employed, as will hereinafter be more fully described.

After the air blast, the coated valve is cooledo'r permitted to cool. The excess flux may be removed as by washing, forexample, of the coated valve. Water or other quenching media may be employed to cool the coated valve. Generally it is preferable to air cool the valve below 800 F. followed by a water quench.

As indicated above, rinsing of the valve inthe molten salt-flux usually serves to drain a substantialportionof the excess aluminum from the valve. However, the amount-- of aluminum remaining provides an aluminum overlay between 0.005 inch and' 0.0l inch thick. In fact, the resultant irregular coating may be even thicker at localized areas, ranging as thick as 0.025 inch. Ashoreinbefore explained, such a coating layer'is" much too heavy to properly protect the base metal of the valve since it tends to crack, check and spell duringv v'alve operation, thereby permitting erosion of the base metal under the protective coating. Therefore, inorder to produce a uniform aluminum coating on the surface and to accurately control the thickness of the intermediate iron-aluminum alloy layer, the valves are air blasted to remove excess 4 molten aluminum and provide a smooth surface at the coating locations.

If the procedure hereinafter described is followed in coating ferrous base poppet valves, the resultant ironaluminum alloy layer ranges from approximately 0.0005 inch to 0.0015 inch in thickness, while the thickness of the aluminum overlay does not exceed about 0.004 inch. It is preferred to have the outer aluminum layer between 0.0005 and 0.0015 inch thick, however, resulting in a combined thickness of the iron-aluminum alloy layer and the aluminum overlay of approximately 0.001 to 0.0025 inch. A coating layer of this thickness has demonstrated superior yielding characteristics when the valve seating face is pounded in during service. Small depressions in the seating face of the valve caused by engine deposits which become lodged between the valve seating face and valve seat during operation remain protected by the surface alloy layer.

Referring more particularly to the drawing, Figure 1 shows a fixture which is especially designed to remove surplus molten aluminum from the head of a poppet valve, thereby producing. a uniform and smooth aluminum coating on the valve surfaces and accurately controlling the thickness of, the intermediate iron-aluminum alloy layer. The outer side walls of this device are formed by a generally cylindrical outer sleeve 10 which preferably has its inner surface internally threaded near its upper end, as indicated at 12. Asecond generally cylindrical sleeve 14 of smaller diameter than the outer sleeve is coaxially positioned within the latter and forms the inner side walls of the unit.

As shown in Figure 2, these two sleeves, each of annular cross-section, are spatially separated radially to form an axially extending air passage or duct 16 which functions as an air pressure equalizer chamber. A flange 18 extends radially outwardly from the bottom end of the inner sleeve 14 and has its outerperipheral edge secured to the lower edge of the outer sleeve 10 by silver soldering or other suitable means,as shown at This flange thereby forms'an annular lower end wall for the unit and seals the passage 16 at its lower end.

An adjustable insert or head 22 is attached to the upper end of the outer sleeve 10, as best seen from Figure 1. This adjustable head isshown as comprising a generally cylindrical body or wall portion 24 which is provided at its upper edge with an integral flange 26 extending radially outwardly therefrom. External threads 28 formed on the outer surfaces of the body portion 24 engage the internal threads 12 on the cylindrical outer sleeve 10 to secure the head thereto and to provide it with longitudinal adjustability relative to the sleeve. The lower end surface 30 of the wall of the head 22 is shown as angularly arranged with respect to the axis of the concentric sleeves. Likewise, the upper end 32 of the inner sleeve 14 is provided with a similar obliquely sloping surface which, when the adjustable head is fastened in position, is spatially separated from the end surface 30 of the head, thereby defining an angularly extending orifice 34 therebetween.

In the embodiment of the invention shown in the drawing, this annular orifice is of a frusto-conical shape and extends from the duct 16 radially inwardly and down wardly to the generally cylindrical central chamber 36 defined by the inner sleeve 14 and the adjustable head 22. A set screw- 38, which contacts the upper end surface of the outer sleeve 10, may be provided in the upper flange 26. This set screw is loosened to permit axial or vertical adjustment of the head 22 so that the orifice size may be varied and is tightened to hold the head stationary after adjustment.

An airinlet opening 40 is provided in the annular flange or lower end wall 18- of the unit for admitting air tothe passage 16 defined by the head 22, the outer sleeve 10, the side wall of the inner sleeve 14 and the flange 18. This inlet duct 40 is shown as communicating with an air. supply tube or pipe, indicated generally at 42, by

means of a pipe nipple 44. One end of this nipple may be attached to the flange 18 by silver soldering, as shown at 46, and the other end threadedly or otherwise suitably connected to the air supply pipe. The upper and lower ends of the central chamber 36 function as air outlets for the device. I 1

- A generally centrally located air inlet tube 48, which extends upwardly within the chamber 36, also may be connected to the air supply pipe 42. This tube extends to within a short distance of the head of a poppet valve when the latter is properly positioned within the chamber 36. The distance between the end of the tube 48 and the valve head should be sufliciently small so that the upward air blast from the'tube does not produce excessive turbulence with the downcoming air jet near the valve seating face. 1

In accordance with the invention, after the poppet valve 50 has been coated with aluminum and, if desired, some of the excess aluminum has been removed in the salt bath, the valve is inserted head downwardly into the passage 12. This is done, of cours, before the aluminum has completely solidified, the coating being in a semi-molten or mushy condition. -When' the poppet valve, is in proper position,- as 'shown in the drawing,

the valve seating face 52 is in the direct line of travel of air passing through the annular orifice 34. In this mannerair which is forced under pressure through the pipe 42 enters the air inlet opening 40, passes through the annular passage 16 and the orifice 32, and impinges upon the valve seating face, thereby aiding in removing excess molten aluminum which still remains. Due to the angle of the valve seating face, a large proportion of the air is directed over the upper surface of the valve head and along the aluminum-coated neck of the valve stem. Thus, surplus aluminum is blown from all these portions of the valve by a single annular jet or stream of air. In like manner, air which is forced upwardly through the central air inlet tube 48 is forcibly projected against the end face of the valve head and removes excess molten aluminum from the surface thereof. The coating metal removed from the valves falls through the central chamber 36 and out of the bottom of the device.

The orifice 34 is" preferably arranged to'direct the compressed air generally normal to the valve seating face. Hence theorifice passage is shown as being at a 45 angle relative to the valve axis. For optimum results, it has been found desirable to locate the valve so that the air impinges against its seating face approximately inch from the edge of this face nearest the valve stem. 1 r

' Of course, it is desirable to provide a more or less permanent means for mounting the poppet valve in proper stationary position within the central chamber-36. This can be done by holding the valve in a suitable clamp 54 attached to the device or otherwise properly located relative to it. It is preferable to design the clamping means to engage the ring grooves normally provided near the ends of poppet valve stems since, in this manner, a series of valves all may be maintained in the same relative position within the chamber. In accordance with the invention, therefore, the valve is not subject to whipping or other movement while it and the coating metal are still red hot during the air blast, but is held fast in a vertical position.

Only the seating face of the poppet valve shown in the drawing has been coated, as indicated by the stippled area of Figure 1. When only this portion of the poppet valve is provided with the coating, it is not necessary to use the central air inlet tube 48 since excess coating material need not be removed from the end face of the valve head. Moreover, even if this end face is coated, the air passing through the annular orifice 34 provides an air foil effect which removes much of the excess coating material from the end face of the valve head. Of course, the distribution or thickness of the coating on the valve end face is not critical from the standpoint of fitting with mating parts since this portion of the valve does not contact any part of the engine in which it is used. The only problem,'.. therefore, is'that of flaking off or spalling of the coating on the head end face of the valve if this coating is excessively thick. Because of the aforementioned air foil effect, however, the central air inlet tube, 48 appears to be necessary only when the head end faces of large size poppet valves are being coated or when the valve heads have concave end surfaces, as is frequently the case with intake valves.

It will be noted that the inner sleeve 14 has a reduced diameter at its lower end, as shown at 56, to provide for lateral enlargement of the air passage or chamber 16 at its lower end and form air inlet opening 40 of suitable size. The formed annular manifold 58 also helps promote the equalization of air pressure within the passage 16 before the air passes through the orific and impinges on the coated valve seating face. Of course, this elfect likewise may be produced by means of a manifold base plate attachment which is not integral with either of the sleeves. Air pressure equalization is further assured by the location of the air inlet opening 40 at an'appreciable distance axially from the annular outlet or orifice 34 and by the angular arrangement of this orifice which necessitates substantial reversal of the direction of air flow before the air contacts the valve.

In this manner the air is evenly distributed throughout the periphery of the orifice while passing therethrough and, by positively removing the excess aluminum and providing a smoothing or leveling effect, results in a smooth, even, thin aluminum coating on the valve seating face. Thus the abovedescribed device for removing excess molten aluminum from. poppet valves provides a uniform air blast on all surfaces of the valve head without having to subject the valve to rotational or other undesirable movement.

Adjustability of the size of the annular orifice 34 permits regulation of the volume of air passing through the orifice per unit time and the velocity of this air stream. For optimum results it is desirable that the air pressure in the line supplying air to the orifice be maintained between approximately 75 and 110 pounds per square inch, a pressure of pounds per square inch, for example, providing excellent results. An air blast of /2 to 4 seconds duration is preferred, and it never need be longer than ten seconds. After this period of time the aluminum coating on the seating face of the poppet valve will have soliidfied. Other gases or vapors could be used to provide the high-velocity jet for removing the surplus coating metal, of course, but compressed air is least expensive and highly effective.

It will be appreciated, of course, that when the same fixture is used for processing different size valves the air pressure and orifice size should be adjusted accordingly. Inasmuch as the criticality of the aluminum coating is restricted primarily to the valve seating face, a poppet valve having a relatively large diameter head necessarily should be subjected to an air stream having a somewhat lower air pressure than a valve having a lesser diameter head where the same fixture is used to remove excess coating metal from the seating faces of valves of both sizes. Best results are obtained, however, when the diameter of the inner sleeve is approximately inch larger than the diameter of the valve head.

As a result of the above-described treatment, a uniform aluminum coating is provided on the appropriate surfaces of the poppet valve, and the thickness of this coating may be carefully regulated. In turn, the thickness of the intermediate iron-aluminum alloy layer may be controlled and, as hereinbefore described, it is this alloy layer which is primarily determinative of the life of the valve. Moreover, not only is the resultant aluminum 7 overlay uniformly thin and-a thin; ev'e'n'inte'rme'diate aluminum-iron alloy layerproduced, but the dimensionsof the seating faces: of the valves so processed will not be disadvantageously' affected during removal of the sur plus molten coating material;

The thin coating thusprovidedon apoppet valve head eliminates the possibility of run-down-of' the coating metal due to melting'while the valveis irfoperation in an engine. Anint'er-ference fit at the valve-seating area-might otherwise result. Moreover, the non-uniform coating which is normally 'produced'if theabove procedure is not followedprevents proper installation of a valve. in an: engine because the" valve seat facing does not conform to the valve seat.

While this invention has been described-by means of certainspecific examples, it will be understood that the scope of the inventionisno't to be limited thereby except as defined in the following-claims.-

I? claim:

1-. A device for removing excess molten coating metal from surfaces of a coatedp'oppet valve, said device comprising a housing havingan inner Wall defining a generally central chamber in which a poppet valve is adapted to be positioned, an annular orifice extending. through said inner wall: adapted to project an annular jet of fluid against the seating face of a3 poppet valve positioned with in. said chamber in a direction generally perpendicular thereto, wall means surrounding said wall defining an enclosed annular fluid passage outwardly of said orifice a tube extending. into-'said'chamb'e'r for directing a second jet of fluid against the head end face of said valve generally perpendicular thereto and centrall y't'hereof', means for supplying said' fluid under pressure'to'said'orifice and said tube, and means for supporting said valve within said chamber.

2. A device for removing excessmol-t'en coating metal from the headof a coated poppet valve, said device comprising a' housing havingconcentricallyarranged, generally cylindrical inner and outer walls which'are spatially separated radially to" provide an annular fluid passage therebetween, wallmeian's sealing-the ends of said passage, said inner wall defining a'- chamber having open ends for receiving at coated poppetyalve, an annular orifice extending throughout the periphery of said inner wall from said passage to said chamber for directing a stream of fluid under pressure'againstth'e seating face of said valve in a direction generally perpendicular to said seating face, a tube extending into said chamber and generally coaxial therewith for conveying'a" second stream of fluid under pressure against the head end faceof said'valve in a direction which is approximatelyperpendicular to said end face, means for supplying. fluid under pressure to said passage and saidtube, and means for retaining said poppet valve stationary within said housing.

3. An apparatus for use' immediately after aluminum dipcoating of a poppet valve to remove excess molten aluminum from the head thereof, said apparatus comprising a housing having generally cylindrical inner and outer walls which are spatially separated radially to provide an annular air passage therebetween, an end wall sealing the bottom'of said passage, an air inlet duct communicating with said passage for introducing air under pressure thereto, a cap which isaxially adjustable relative to-said' hous'ing secured to the upper end thereof, said cap and the upper end of said inner wall being spatially separated to define an interjacent annular orifice adapted to project a stream of air under pressure inwardly and downwardly against a seating face of a poppet valve positioned within the chamber defined' by said inner wall means for supporting said valve within said chamber, and anair inlet tube extending upwardly into said chamber for directing a streamof compressed air against the head end face of said'valve in a direction generally perpendicular thereto and centrally thereof.

4. An apparatus for use immediately after dip coating a poppet valve with aluminum'to remove excess molten aluminum therefrom, said apparatus comprising an elongated housing having inner andouter cylindrical walls which are spatially separated radially to provide an annular air passage therebetween, said inner wall-having an opening extending axially therethrough, a Wall sealing the lower end of said passage, an air inlet duct communicating with said passage for conveying compressed air thereto, an adjustable cap secured to the upper end of said housing sealing the upper end of saidpassag means for clamping a poppet valve stationary within said opening, said sleeve beingaxially adjustable relative to said inner wall, said cap and-the upper end of said inner cylindrical wall being spatially separated to define an interjacent annular air orifice adapted to direct a stream of compressed air throughout the entire inner circumference of said orifice radially inwardly and downwardlyagainst the seating face of said valve, an air inlet tube extending upwardly into said opening for directing. a stream of compressed air against the head-end face of said valve, and means for supplying compressed air to said tube.

References Cited in the file of: this patent 

